BELT CONVEYOR STANDARDISATION AN AID TO MINE PLANNING

BELT CONVEYOR STANDARDISATION AN AID TO MINE PLANNING

  1. INTRODUCTION
    Tremendous progress and capital investment has been made in recent years in the
    development of coal production equipment for both longwall and room and pillar installations. This progress has inevitably resulted in considerable increase in mine outputs. In many instances, this improvement in efficiency in the production area, has highlighted the inefficiency of outbye belt conveyor systems.
    As a result of these improvements, the requirements of the mining industry have
    been reviewed and schemes to suit the demands of increased productivity have been
    developed. Within these developments, particular attention has been devoted to the
    standardisation of equipment.
    Many papers have been written on the subject of the transportation of materials and
    equipment and therefore, the author is confining this study to the following subjects
    relating to the transportation of minerals and personnel by belt conveyor.
    a) Conventional Belt Conveying equipment
    b) Extensible Belt Conveyors
    c) Man-riding Conveyors
    d) Booster Conveyors
    e) High Powered Conveyors
  2. CONVENTIONAL CONVEYING EQUIPMENT
    2.1. Drive Equipment
    The need to improve the design and increase the power range of the drive equipment
    to meet the developing requirements of the coal industry, the following main criteria are
    found important.
    a) Maximum efficiency
    b) Minimum maintenance
    c) Economical
    d) Dimensionally compact
    e) Safe in operation
    f) Compact standardisation
    These parameters culminated in the design of drive equipment with power ratings in
    the 48-560 KW range.
    The drive heads are ‘slimline’ design to suit the limitations of narrow roadways and
    are modular construction for ease of underground transportation and assembly. The
    complete unit comprises individual drum units, power units and reduction gearboxes.
    Each module is machine faced or spigot mounted for ease of assembly and in the unlikely
    event of breakdown, the drive pulleys can be withdrawn through the side of the pulley
    unit without disturbing the drive structure.
    The spigot mounted gearbox is standard to the total range of the drive equipment
    and this feature also applies in many cases to the drive pulleys and pulley units, which
    within certain power ranges, are interchangeable.
    The power units can be fitted with either foot or flange-mounted motors and a variety
    of couplings, brakes, or backstops is available to suit customer requirements.
    Facilities are also available to monitor the condition of the bearings, the temperature
    of gearbox oil, the wear of brake linings, etc.
    A comprehensive range of delivery ends is available for all types of discharge which
    include adjustable delivery pulleys and suitable belt scrapers.
    One of the major problems associated with belt conveying systems is that of cleaning
    the dirt and moisture from the return belt to avoid ‘build-up’ at each pulley and return
    idler location. To solve this problem a dirt disposal conveyor fitted to the underside of
    the delivery end has been innovated. This unit, together with the incorporation of multiple belt scrapers, has proved invaluable in improving the performance of conveyor
    systems.

2.2. Belt Tensioning & Storage Equipment
In order to ensure that adequate tension is applied to return strand of the conveyor
belt, to maintain suitable driving tension, a tensioning unit is normally installed at the
rear of the drive head. Several types of units are available for this purpose, each being
capable of storing a nominal quantity of belt, the length of the unit naturally varying
with the length of the conveyor installation.
The various types of the belt tensioning equipment are as follows.
The Hand Winch Type is the commonest form of unit, being the most economical,
the tension being manually applied by means of hand operated winches which are rope
coupled to the mobile tension carriage.
The Gravity Type is a more effective unit incorporating structure as the hand winch
type, but with the tension carriage ropes coupled to a ‘floating’ weight frame within a
tower which is located adjacent to the rear section. The weights automatically control
the elastic stetch of the conveyor belt and as permanent stetch occurs, the hand winches
are used to adjust the position of the weight frame within the tower.
The Automatic Type is a more sophisticated system with the same type of structure
as the above units, but with an electrick winch replacing the hand winches. The winch is
bolted onto the rear loop structure and is rope coupled through the mobile tension carriage to a dynamometer. The dynamometer is ‘set’ to suit the requisite belt tension and
control the tension by means of switches within the dynamometer which actuate intermediate control relays, which in turn, operate a forward or reserve contactor controlling the electric winch motor. This action has the effect of releasing belt when in a state of overtension and ‘reeling in’ belt when slack occurs
The Hydraulic Unit is a patented design, which automatically maintains the required
conveyor driving tension with a similar response to that of a gravity system.
In operation, belt tension is maintained by the charge in the accumulators which
discharge to the actuator when the conveyor is started and slack belt develops. The process is reversed when the conveyor is stopped, when the return belt tension tends to
increase.
2.3. Belt Conveyor Structure
Belt conveyor structures are so variant in design and type that they are too numerous
to discuss effectively.
It can be stated, however, that the most popular is the tubular boltless type due to its
ease of assembly and is less prone to fines ‘build-up’ than other conventional structures.
The same reference can be made to loading sections and return end units. In this
instance the most popular is the modular construction type which can be fitted with a
variety of impact idlers and includes a fines drawer to facilitate the removal of fines
from the return pulley frame The idler rollers are of a standard design.

  1. EXTENSIBLE CONVEYORS
    In all mining operations, the main objective is to achieve maximum output in the
    minimum period. To achieve this ideal, mining should be a continuous operation, but
    regrettably, is unattainable. The introduction of extensible belt conveying systems has
    contributed to an improvement in the loading cycle.
    The conventional method of extending conveyors is by the addition of conveyor sections at the return end and the insertion of an appropriate length of belt.
    Although this is a relatively simple operation, it is time consuming and adding multiples of belt has its obvious disadvantages.
    An alternative method is to apply an overlapping conveyor, generally a stage loader.
    With this system a degree of continuity is attained, but when the overlap is exhausted,
    the return end must be pulled back prior to adding sections and belt.
    The preferred system comprises a long skid mounted return end which forms the
    track for either a Stage Loader or Bridge Conveyor Support Trolley. The trolley is fitted
    with a horizontal and vertical articulated frame to accomodate deviations in the roadheader or continuous miner operation. The system operates in conjunction with an
    automatic storage type loop take-up unit. As the ‘getting’ machine advances, the trolley,
    including the mobile receiving section moves towards the rear of the return end. When
    the length of travel is taken up, the return end is retreated until the trolley is stuated at
    the front of the track. The action of retreating the return end creates overtension in the
    belt. The overtension reaction is detected by the dynamometer in the extensible loop
    take-up. The dynamometer then actuates the electric winch which allows belt to be
    released from the storage area. On completion of the cycle, the dynamometer detects
    the slack belt condition an dictates that the winches ‘reels in’, to ensure that the correct
    drive tension is maintained. The storage loop is capable of storing up to 100 metres of
    belt, ensuring that the operation can be continuous for a lengthy period.
    Further developments within this area include the introduction of an Angle Station
    which permits the belt to negotiate angular turns without misalignment.
  2. MAN-RIDING CONVEYORS
    Due to improvements in modern mining techniques and the associated increase in the
    rate of advance of mechanised faces, it follows that the distance to the coal face is also
    increasing. This situation introduces the problem of transporting personnel to their place
    of work as quickly as possible, to ensure that they arrive in a fit condition and that the
    maximum time will be available for output during the shift.
    In relation to the rapid face advance referred to, longer trunk and gate belt conveyors
    are being installed and consequently, the practice of riding personnel on conveyor belt is
    increasing. Although the use of belts for man-riding was formerly forbidden by the Mines
    Inspectorate because of the hazards involved, the practice is now completely legalised as
    a result of the introduction of the necessary safety equipment. Details of the Codes and
    Rules of Practice are available in booklet form from the UK’s National Coal Board’s Production Department. This deals with all aspects of safety, details of relevant clearances
    and equipment, including boarding and alighting platforms, safety gates, emergency trip
    wire systems, etc.
    Conveyor man-riding has significant advantages over other conventional systems;
    a) There is no waiting time at the beginning or end of the working shift, being a continuous operation.
    b) Where conveyors are already installed for mineral transport, these can be easily
    adapted for man-riding, with the addition of boarding and alighting platforms, safety
    gates and signalling equipment, which in many instances, is already fitted to the conveyor structure.
    The practice of man-riding was initially confined to riding on the top belt, but doubledecked structure for top and bottom belt man-riding is now commonplace. Statistics are
    available showing the substantial time saving due to the introduction of man-riding on
    belt conveyors.
    The development of these systems is constantly being reviewed, particulary with respect to safety and increased speeds. It is noteworthy that when beld man-riding was
    officially introduced in the late 60’s, the maximum allowable speed was 1.88 m/second,
    whereas the current speed is 2.66 m/second.
    It must be emphasised that at no time has the safety of personnel been sacrificed for
    the desired increase in speed. This fact is substantiated by statistics which indicate that
    in UK Mines, accidents relating to belt man-riding is much less than any other form of
    underground transport. The highest rate is attributed to men walking the roadways.
    5. BOOSTER CONVEYORS
    During recent years, the demands on mineral transport systems have increased, due
    to improvements in production rates and extending lengths of conveyor systems. This is
    particulary appropriate to longwall developments. The requirements associated with
    these improvements have been identified and as the development of belting technology
    has enabled higher tensile ratings to be available, the necessary belt conveying equipment
    to meet these demands have also been developed.
    Situations can arise, however, where it is uneconomical to introduce new equipment
    and belting for a variety of reasons. It was because of these factors the application of
    the concept of adding increased power into a belt conveyor at an intermediate point/s
    were investigated and developed. This system has become universally known as the
    booster drive.
    The booster drive has been designed so that it can be installed at a suitable selected
    point between the delivery and return pulleys, of an existing belt conveyor installation.
    In constrast to the conventional mode of power transference to the conveyor belt, by
    wrapping the belt around a single or series of driving pulleys, the booster drive transmits
    the tractive force linearly, by frictional contact with the main belt. The power transmitting element is an endless driving belt, which is in contact with the underside of the carrying strand running on the idlers of the main carrying belt.
    The pressure to transmit the force results from a combination of the weight of the
    belt and the material being transported. Although the unit pressure is much less than
    that achieved by the conventional method, the required force is attained by an extended
    length of engagement between the belts.
    This simple method of power transfer, enables the principle of intermediate boostering to be applied to any belt conveyor system and offers the following advantages;
    a) The belt tension is reduced, therefore, a lower tensile strength belt can be used at
    a substantially reduced capital cost.
    b) Individual conveyor lengths can be increased.
    c) In-line transfer points can be eliminated thus reducing degredation of mineral and
    the hazards associated with airborne dust.
    d) The physical size of the equipment is reduced thereby obviating the need for costly
    excavations.
    e) Common components can be utilised thus reducing spares holdings and associated
    maintenance.
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    f) Where belt man-riding is practiced, the frequency of boarding and alighting is reduced, which improves overall efficiency
    g) The handling capacity of the conveyor can be increased.
    h) In the event of a transmission failure on a drive unit, the system could still operate,
    although at a reduced capacity.
    The application of booster drives fall into four main categories;
    a) To increase the carrying of an existing conveyor system. This particularly applies
    in the mining industry where production rates are being improved due to increased
    mechanisation and the increasing use of equipment to higher technological standards.
    b) To increase the length of an existing conveyor system. Again applicable to underground mining situations where the distance between the point of mineral extraction
    and the point of egress from the mine is continually increasing.
    c) To eliminate intermediate transfer points in an existing series of in-line conveyors,
    by converting some of the existing drives into intermediate booster drives.
    d) In any new belt conveyor scheme where site conditions and other considerations
    such as standardisation of equipment, standardisation of grade of belt, capital costs of
    equipment, belt and spares, running costs and maintenance costs indicate that a booster
    system would be the most beneficial arrangement.
    Details are available showing the varying conditions to which “boosters” are applied,
    which once again, demonstrates the high degree of standardisation of equipment involved.
    6. HIGH POWERED BELT CONVEYORS
    There has been considerable development in recent years relating to the application
    of high powered belt conveyors. The principal factor has been in the continual improvement in the tensile capability of both fabric and steel cord conveyor belting.
    These improvements now enable conveyor designers to develop very long centre,
    single flight conveyors, involving high vertical lifts. This feature has led to the introduction of single slope conveyors capable of dealing with the total output of the mine in
    preference to shaft winding systems.
    With this type of application, it becomes increasingly difficult to utilise standart equipment. However, there are many installations in the UK and overseas, where the systems
    have been designed to include standard major components. This applies particularly to
    gearboxes, pulleys and main bearings. It is understandable that the associated drive supporting structure varies considerably with each application.
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    7. CONCLUSION
    It is difficult to deal adequately with the subject of standardisation benefits for face
    to surface equipment in the limited space and time available. To refer to the original
    comment, the development of coal production equipment has revolutionised the industry.
    We must, therefore, ensure that the outbye systems are capable of accommodating the
    resultant increased output.
    In developing these systems, management must be increasingly aware of the need,
    wherever possible, to give serious consideration to “Conveyor Standardisation — an Aid
    to Mine Planning”.

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